The present invention relates to an improved disk clamping device for clamping either a disk having a small diameter hole, such as a compact audio disk (CD) which has both a small outside diameter and small center hole size, or a disk having a large hole diameter, such as a video disk (LD), onto the turntable of a disk player so that disks of large and small hole diameters may be played with one disk player.
A conventional disk clamping device for playing both CDs and LDs will be described with reference to FIGS. 1 through 3.
In FIG. 1, reference numeral 6 designates an electric motor. A turntable 2 is fixedly mounted on the output shaft 5 of the motor 6. A centering hub 4, including both a CD hub 4a and LD hub 4b arranged in two stages, is movably mounted on the output shaft 5 with a compression spring 11 interposed between the centering hub 4 and the turntable 2.
A clamper 1 is mounted above the shaft 5 movable vertically. The clamper 1 is used to push a CD 3 or LD 10 against the turntable 2 from above.
Signals recorded on the CD 3 or LD 10 are read with a light beam 9 emitted through an objective lens 8 of an optical pickup 7.
In the disk clamping device, as shown in FIG. 2, the center hole of the CD 3 is engaged with the CD hub 4a of the centering hub 4. Under this condition, the clamper 1 is moved downwardly so that the CD 3 is pushed against the turntable 2 while the compression spring 11 is compressed. Then, the CD 3 is rotated by the motor 6.
In the case of the LD 10, as shown in FIG. 3, its center hole is engaged with the LD hub 4b of the centering hub 4. Similar to the case of the CD 3, the clamper 1 is moved downwardly so that the LD 10 is fixedly held between the clamper 1 and the turntable 2. The LD 10 thus held is rotated by the motor 6.
In FIG. 2, reference character L designates the radius of the innermost signal area on the CD 3.
The maximum outside diameter allowed for the turntable 2 is L-l, where l is the dimension between the center of the light beam 9 and the side of the pickup 7 closest to the shaft 5. For recent pickups, the dimension l is about 22 mm or less.
As is well known, the turntable 2 provides the foundation for clamping a CD 3 or LD 10. Therefore, as the diameter of the turntable 2 is decreased, the amount of vibration and bending of the disk as it is rotated is increased, as a result of which the light beam ultimately cannot be focused on the surface of the disk. When this occurs, the reproduced signals are low in quality; that is, the output picture or sound is of low quality. At the same time, the vibration of the overall disk player is also increased for the same reason, which further lowers the quality of the output signals.
In addition, when a disk is clamped, the clamping error is increased, and the angle of inclination of the CD 3 or LD 10 with respect to the turntable 2 is increased. This difficulty is more significant for the LD 10 which is larger in outside diameter than the CD 3.